Network Working Group B. Sarikaya
Internet-Draft Denpel Informatique
Intended status: Best Current Practice L. Dunbar
Expires: February 10, 2019 Huawei USA
B. Khasnabish
ZTE (TX) Inc.
T. Herbert
Quantonium
S. Dikshit
Cisco Systems
August 9, 2018
Virtual Machine Mobility Protocol for L2 and L3 Overlay Networks
draft-ietf-nvo3-vmm-04.txt
Abstract
This document describes a virtual machine mobility protocol commonly
used in data centers built with overlay-based network virtualization
approach. For layer 2, it is based on using a Network Virtualization
Authority (NVA)-Network Virtualization Edge (NVE) protocol to update
Address Resolution Protocol (ARP) table or neighbor cache entries at
the NVA and the source NVEs tunneling in-flight packets to the
destination NVE after the virtual machine moves from source NVE to
the destination NVE. For Layer 3, it is based on address and
connection migration after the move.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 10, 2019.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of the protocol . . . . . . . . . . . . . . . . . . 4
4.1. VM Migration . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Task Migration . . . . . . . . . . . . . . . . . . . . . 6
4.2.1. Address and Connection Migration in Task Migration . 7
5. Handling Packets in Flight . . . . . . . . . . . . . . . . . 8
6. Moving Local State of VM . . . . . . . . . . . . . . . . . . 9
7. Handling of Hot, Warm and Cold Virtual Machine Mobility . . . 9
8. Virtual Machine Operation . . . . . . . . . . . . . . . . . . 10
8.1. Virtual Machine Lifecycle Management . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . 11
13.2. Informative references . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Data center networks are being increasingly used by telecom operators
as well as by enterprises. In this document we are interested in
overlay-based data center networks supporting multitenancy. These
networks are organized as one large Layer 2 network geographically
distributed in several buildings. In some cases geographical
distribution can span across Layer 2 boundaries. In that case need
arises for connectivity between Layer 2 boundaries which can be
achieved by the network virtualization edge (NVE) functioning as
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Layer 3 gateway routing across bridging domain such as in Warehouse
Scale Computers (WSC).
Virtualization which is being used in almost all of today's data
centers enables many virtual machines to run on a single physical
computer or compute server. Virtual machines (VM) need hypervisor
running on the physical compute server to provide them shared
processor/memory/storage. Network connectivity is provided by the
network virtualization edge (NVE) [RFC8014]. Being able to move VMs
dynamically, or live migration, from one server to another allows for
dynamic load balancing or work distribution and thus it is a highly
desirable feature [RFC7364].
There are many challenges and requirements related to migration,
mobility, and interconnection of Virtual Machines (VMs)and Virtual
Network Elements (VNEs). Retaining IP addresses after a move is a
key requirement [RFC7364]. Such a requirement is needed in order to
maintain existing transport connections.
In L3 based data networks, retaining IP addresses after a move is
simply not possible. This introduces complexity in IP address
management and as a result transport connections need to be
reestablished.
In view of many virtual machine mobility schemes that exist today,
there is a desire to define a standard control plane protocol for
virtual machine mobility. The protocol should be based on IPv4 or
IPv6. In this document we specify such a protocol for Layer 2 and
Layer 3 data networks.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119] and
[RFC8014].
This document uses the terminology defined in [RFC7364]. In addition
we make the following definitions:
Tasks. Tasks are the generalization of virtual machines. Tasks in
containers that can be migrated correspond to the virtual machines
that can be migrated. We use task and virtual machine
interchangeably in this document.
Hot VM Mobility. A given VM could be moved from one server to
another in running state.
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Warm VM Mobility. In case of warm VM mobility, the VM states are
mirrored to the secondary server (or domain) at a predefined
(configurable) regular intervals. This reduces the overheads and
complexity but this may also lead to a situation when both servers
may not contain the exact same data (state information)
Cold VM Mobility. A given VM could be moved from one server to
another in stopped or suspended state.
Source NVE refers to the old NVE where packets were forwarded to
before migration.
Destination NVE refers to the new NVE after migration.
Packets in flight refers to the packets received by the source NVE
sent by the correspondents that have old ARP or neighbor cache entry
before VM or task migration.
Users of VMs in diskless systems or systems not using configuration
files are called end user clients.
3. Requirements
This section states requirements on data center network virtual
machine mobility.
Data center network SHOULD support virtual machine mobility in IPv6.
IPv4 SHOULD also be supported in virtual machine mobility.
Virtual machine mobility protocol MAY support host routes to
accomplish virtualization.
Virtual machine mobility protocol SHOULD not support triangular
routing except for handling packets in flight.
Virtual machine mobility protocol SHOULD not need to use tunneling
except for handling packets in flight.
4. Overview of the protocol
Layer 2 and Layer 3 protocols are described next. In the following
sections, we examine more advanced features.
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4.1. VM Migration
Being able to move Virtual Machines dynamically, from one server to
another allows for dynamic load balancing or work distribution and
thus it is a highly desirable feature. In a Layer-2 based data
center approach, virtual machine moving to another server does not
change its IP address. Because of this an IP based virtual machine
mobility protocol is not needed. However, when a virtual machine
moves, NVEs need to change their caches associating VM Layer 2 or
Medium Access Control (MAC) address with NVE's IP address. Such a
change enables NVE to send outgoing MAC frames addressed to the
virtual machine. VM movement across Layer 3 boundaries is not
typical but the same solution applies if the VM moves in the same
link such as in WSCs.
Virtual machine moves from its source NVE to a new, destination NVE.
After the move the virtual machine IP address(es) do not change but
this virtual machine is now under a new NVE, previously communicating
NVEs will continue to send their packets to the source NVE. Address
Resolution Protocol (ARP) cache in IPv4 [RFC0826] or neighbor cache
in IPv6 [RFC4861] in the NVEs need to be updated.
It may take some time to refresh ARP/ND cache when a VM is moved to a
new destination NVE. During this period, a tunnel is needed so that
source NVE forwards packets to the destination NVE.
In IPv4, the virtual machine immediately after the move should send a
gratuitous ARP request message containing its IPv4 and Layer 2 or MAC
address in its new NVE, destination NVE. This message's destination
address is the broadcast address. Source NVE receives this message.
source NVE should update VM's ARP entry in the central directory at
the NVA. Source NVE asks NVA to update its mappings to record IPv4
address of the moving VM along with MAC address of VM, and NVE IPv4
address. An NVE-to-NVA protocol is used for this purpose [RFC8014].
Reverse ARP (RARP) which enables the host to discover its IPv4
address when it boots from a local server [RFC0903] is not used by
VMs because the VM already knows its IPv4 address. IPv4/v6 address
is assigned to a newly created VM, possibly using Dynamic Host
Configuration Protocol (DHCP). Next, we describe a case where RARP
is used.
There are some vendor deployments (diskless systems or systems
without configuration files) wherein VM users, i.e. end-user clients
ask for the same MAC address upon migration. This can be achieved by
the clients sending RARP request reverse message which carries the
old MAC address looking for an IP address allocation. The server, in
this case the new NVE needs to communicate with NVA, just like in the
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gratuitous ARP case to ensure that the same IPv4 address is assigned
to the VM. NVA uses the MAC address as the key in the search of ARP
cache to find the IP address and informs this to the new NVE which in
turn sends RARP reply reverse message. This completes IP address
assignment to the migrating VM.
All NVEs communicating with this virtual machine uses the old ARP
entry. If any VM in those NVEs need to talk to the new VM in the
destination NVE, it uses the old ARP entry. Thus the packets are
delivered to the source NVE. The source NVE MUST tunnel these in-
flight packets to the destination NVE.
When an ARP entry in those VMs times out, their corresponding NVEs
should access the NVA for an update.
IPv6 operation is slightly different:
In IPv6, the virtual machine immediately after the move sends an
unsolicited neighbor advertisement message containing its IPv6
address and Layer-2 MAC address in its new NVE, the destination NVE.
This message is sent to the IPv6 Solicited Node Multicast Address
corresponding to the target address which is VM's IPv6 address. NVE
receives this message. NVE should update VM's neighbor cache entry
in the central directory of the NVA. IPv6 address of VM, MAC address
of VM and NVE IPv6 address are recorded in the entry. An NVE-to-NVA
protocol is used for this purpose [RFC8014].
All NVEs communicating with this virtual machine uses the old
neighbor cache entry. If any VM in those NVEs need to talk to the
new VM in the destination NVE, it uses the old neighbor cache entry.
Thus the packets are delivered to the source NVE. The source NVE
MUST tunnel these in-flight packets to the destination NVE.
When a neighbor cache entry in those VMs times out, their
corresponding NVEs should access the NVA for an update.
4.2. Task Migration
Virtualization in L2 based data center networks becomes quickly
prohibitive because ARP/neighbor caches don't scale. Scaling can be
accomplished seamlessly in L3 data center networks by just giving
each virtual network an IP subnet and a default route that points to
NVE. This means no explosion of ARP/ neighbor cache in VMs and NVEs
(just one ARP/ neighbor cache entry for default route) and there is
no need to have Ethernet header in encapsulation [RFC7348] which
saves at least 16 bytes.
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In L3 based data center networks, since IP address of the task has to
change after move, an IP based task migration protocol is needed.
The protocol mostly used is the identifier locator addressing or ILA
[I-D.herbert-nvo3-ila]. Address and connection migration introduce
complications in task migration protocol as we discuss below.
Especially informing the communicating hosts of the migration becomes
a major issue. Also, in L3 based networks, because broadcasting is
not available, multicast of neighbor solicitations in IPv6 would need
to be emulated.
Task migration involves the following steps:
Stop running the task.
Package the runtime state of the job.
Send the runtime state of the task to the destination NVE where the
task is to run.
Instantiate the task's state on the new machine.
Start the tasks for the task continuing from the point at which it
was stopped.
Address migration and connection migration in moving tasks are
addressed next.
4.2.1. Address and Connection Migration in Task Migration
Address migration is achieved as follows:
Configure IPv4/v6 address on the target host.
Suspend use of the address on the old host. This includes handling
established connections. A state may be established to drop packets
or send ICMPv4 or ICMPv6 destination unreachable message when packets
to the migrated address are received.
Push the new mapping to hosts. Communicating hosts will learn of the
new mapping via a control plane either by participation in a protocol
for mapping propagation or by getting the new mapping from a central
database such as Domain Name System (DNS).
Connection migration involves reestablishing existing TCP connections
of the task in the new place.
The simplest course of action is to drop TCP connections across a
migration. Since migrations should be relatively rare events, it is
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conceivable that TCP connections could be automatically closed in the
network stack during a migration event. If the applications running
are known to handle this gracefully (i.e. reopen dropped connections)
then this may be viable.
More involved approach to connection migration entails pausing the
connection, packaging connection state and sending to target,
instantiating connection state in the peer stack, and restarting the
connection. From the time the connection is paused to the time it is
running again in the new stack, packets received for the connection
should be silently dropped. For some period of time, the old stack
will need to keep a record of the migrated connection. If it
receives a packet, it should either silently drop the packet or
forward it to the new location, similarly as in Section 5.
5. Handling Packets in Flight
Source hypervisor may receive packets from the virtual machine's
ongoing communications and these packets should not be lost and they
should be sent to the destination hypervisor to be delivered to the
virtual machine. The steps involved in handling packets in flight
are as follows:
Preparation Step It takes some time, possibly a few seconds for a VM
to move from its source hypervisor to a new destination one.
During this period, a tunnel needs to be established so that the
source NVE forwards packets to the destination NVE.
Tunnel Establishment - IPv6 Inflight packets are tunneled to the
destination NVE using the encapsulation protocol such as VXLAN in
IPv6. Source NVE gets destination NVE address from NVA in the
request to move the virtual machine.
Tunnel Establishment - IPv4 Inflight packets are tunneled to the
destination NVE using the encapsulation protocol such as VXLAN in
IPv4. Source NVE gets destination NVE address from NVA when NVA
requests NVE to move the virtual machine.
Tunneling Packets - IPv6 IPv6 packets are received for the migrating
virtual machine encapsulated in an IPv6 header at the source NVE.
Destination NVE decapsulates the packet and sends IPv6 packet to
the migrating VM.
Tunneling Packets - IPv4 IPv4 packets are received for the migrating
virtual machine encapsulated in an IPv4 header at the source NVE.
Destination NVE decapsulates the packet and sends IPv4 packet to
the migrating VM.
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Stop Tunneling Packets When source NVE stops receiving packets
destined to the virtual machine that has just moved to the
destination NVE.
6. Moving Local State of VM
After VM mobility related signaling (VM Mobility Registration
Request/Reply), the virtual machine state needs to be transferred to
the destination Hypervisor. The state includes its memory and file
system. Source NVE opens a TCP connection with destination NVE over
which VM's memory state is transferred.
File system or local storage is more complicated to transfer. The
transfer should ensure consistency, i.e. the VM at the destination
should find the same file system it had at the source. Precopying is
a commonly used technique for transferring the file system. First
the whole disk image is transferred while VM continues to run. After
the VM is moved any changes in the file system are packaged together
and sent to the destination Hypervisor which reflects these changes
to the file system locally at the destination.
7. Handling of Hot, Warm and Cold Virtual Machine Mobility
Cold Virtual Machine mobility is facilitated by the VM initially
sending an ARP or Neighbor Discovery message at the destination NVE
but the source NVE not receiving any packets inflight. Cold VM
mobility also allows all previous source NVEs and all communicating
NVEs to time out ARP/neighbor cache entries of the VM and then get
NVA to push to NVEs or get NVEs to pull the updated ARP/neighbor
cache entry from NVA.
The VMs that are used for cold standby receive scheduled backup
information but less frequently than that would be for warm standby
option. Therefore, the cold mobility option can be used for non-
critical applications and services.
In cases of warm standby option, the backup VMs receive backup
information at regular intervals. The duration of the interval
determines the warmth of the standby option. The larger the
duration, the less warm (and hence cold) the standby option becomes.
In case of hot standby option, the VMs in both primary and secondary
domains have identical information and can provide services
simultaneously as in load-share mode of operation. If the VMs in the
primary domain fails, there is no need to actively move the VMs to
the secondary domain because the VMs in the secondary domain already
contain identical information. The hot standby option is the most
costly mechanism for providing redundancy, and hence this option is
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utilized only for mission-critical applications and services. In hot
standby option, regarding TCP connections, one option is to start
with and maintain TCP connections to two different VMs at the same
time. The least loaded VM responds first and pickup providing
service while the sender (origin) still continues to receive Ack from
the heavily loaded (secondary) VM and chooses not use the service of
the secondary responding VM. If the situation (loading condition of
the primary responding VM) changes the secondary responding VM may
start providing service to the sender (origin).
8. Virtual Machine Operation
Virtual machines are not involved in any mobility signalling. Once
VM moves to the destination NVE, VM IP address does not change and VM
should be able to continue to receive packets to its address(es).
This happens in hot VM mobility scenarios.
Virtual machine sends a gratuitous Address Resolution Protocol or
unsolicited Neighbor Advertisement message upstream after each move.
8.1. Virtual Machine Lifecycle Management
Managing the lifecycle of VM includes creating a VM with all of the
required resources, and managing them seamlessly as the VM migrates
from one service to another during its lifetime. The on-boarding
process includes the following steps:
1. Sending an allowed (authorized/authenticated) request to Network
Virtualization Authority (NVA) in an acceptable format with
mandatory/optional virtualized resources {cpu, memory, storage,
process/thread support, etc.} and interface information
2. Receiving an acknowledgement from the NVA regarding availability
and usability of virtualized resources and interface package
3. Sending a confirmation message to the NVA with request for
approval to adapt/adjust/modify the virtualized resources and
interface package for utilization in a service.
9. Security Considerations
Security threats for the data and control plane are discussed in
[RFC8014]. There are several issues in a multi-tenant environment
that create problems. In L2 based data center networks, lack of
security in VXLAN, corruption of VNI can lead to delivery to wrong
tenant. Also, ARP in IPv4 and ND in IPv6 are not secure especially
if we accept gratuitous versions. When these are done over a UDP
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encapsulation, like VXLAN, the problem is worse since it is trivial
for a non trusted application to spoof UDP packets.
In L3 based data center networks, the problem of address spoofing may
arise. As a result the destinations may contain untrusted hosts.
This usually happens in cases like the virtual machines running third
part applications. This requires the usage of stronger security
mechanisms.
10. IANA Considerations
This document makes no request to IANA.
11. Acknowledgements
The authors are grateful to Dave R. Worley, Qiang Zu, Andrew Malis
for helpful comments.
12. Change Log
o submitted version -00 as a working group draft after adoption
o submitted version -01 with these changes: references are updated,
added packets in flight definition to Section 2
o submitted version -02 with updated address.
o submitted version -03 to fix the nits.
o submitted version -04 in reference to the WG Last call comments.
13. References
13.1. Normative References
[RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
.
[RFC0903] Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
Reverse Address Resolution Protocol", STD 38, RFC 903,
DOI 10.17487/RFC0903, June 1984,
.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
.
[RFC7364] Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
Kreeger, L., and M. Napierala, "Problem Statement:
Overlays for Network Virtualization", RFC 7364,
DOI 10.17487/RFC7364, October 2014,
.
[RFC8014] Black, D., Hudson, J., Kreeger, L., Lasserre, M., and T.
Narten, "An Architecture for Data-Center Network
Virtualization over Layer 3 (NVO3)", RFC 8014,
DOI 10.17487/RFC8014, December 2016,
.
13.2. Informative references
[I-D.herbert-nvo3-ila]
Herbert, T. and P. Lapukhov, "Identifier-locator
addressing for IPv6", draft-herbert-nvo3-ila-04 (work in
progress), March 2017.
Authors' Addresses
Behcet Sarikaya
Denpel Informatique
Email: sarikaya@ieee.org
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Linda Dunbar
Huawei USA
5340 Legacy Dr. Building 3
Plano, TX 75024
Email: linda.dunbar@huawei.com
Bhumip Khasnabish
ZTE (TX) Inc.
55 Madison Avenue, Suite 160
Morristown, NJ 07960
Email: vumip1@gmail.com, bhumip.khasnabish@ztetx.com
Tom Herbert
Quantonium
Email: tom@herbertland.com
Saumya Dikshit
Cisco Systems
Cessna Business Park
Bangalore, Karnataka, India 560 087
Email: sadikshi@cisco.com
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